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International Journal of Modern Engineering Research (IJMER)

www.ijmer.com Vol. 3, Issue. 3, May.-June. 2013 pp-1727-1730 ISSN: 2249-6645

www.ijmer.com 1727 | Page

Vakas K. Rahman1, Prof. A. R. Mundhada

2

1PG Student, Department of Civil Engineering, P.R.M.I.T. & R, Badnera, Amravati, India-444701

2Professor, Department of Civil Engineering, P.R.M.I.T. & R, Badnera, Amravati, India-444701

AbstractThis paper presents the comparison of R.C.C. and Prestressed Concrete Flat Slab. This work includes the designand estimates for R.C.C. and Prestressed Concrete flat slabs of various spans. The aim of this work is to design R.C.C. as

well as prestressed concrete flat slabs for various spans and then compare the results. Programming in MS EXCEL is done

to design both types of flat slabs. The idea is to reach a definite conclusion regarding the superiority of the two techniques

over one another. Results reveal that a R.C.C. flat slab is cheaper than pre-stressed concrete flat slab for smaller spans but

vice versa is true for larger spans.

I ndex Terms:Flat Slab, Prestressed Concrete, R.C.C., Column Strip, Middle Strip, Strand.

I. Introduction1.1 Importance & Necessity

Without any semblance of doubt, reinforced cement concrete construction has been the most revolutionaryconstruction technique of modern times. Combining the high compressive strength of concrete with high tensile strength and

elasticity of steel has resulted in a composite material that is strong, durable and economical. Moreover, it is time tested.

One of the greatest assets of homo-sapiens is the quest for excellence. The human being has constantly refused to

sit over his laurels and become complacent. This has often resulted in new invention and improved products and techniques.

Very week tensile strength of concrete lead to discovery of R.C.C. Bulkiness of R.C.C resulted in the invention of shells.

The problem of serviceability associated with the R.C.C. structures sent the human mind working over-time. The solution

was found in prestressing. Like ordinary reinforced concrete, prestressed concrete consists of concrete resisting compressionand reinforcement carrying tension. Prestressing became essential in many applications in order to fully utilize the

compressive strength of reinforced concrete and to eliminate or control cracking and deflection.

The aim of this work is to design Flat Slab of R.C.C. as well as prestressed concrete variety and then compare the

results. The idea is to reach a definite conclusion regarding the Superiority of the two techniques over each other.

1.2

ScopeThis work includes the design and estimate for Flat Slabs of various spans, ranging from 6.0 M to 12.0 M, by R.C.C.

and Prestressed Concrete techniques. For smaller spans, associated with normal building works, prestressed concrete

construction becomes too cumbersome, irrespective of the economics involved. Intensity of assumed loading is kept

sufficient enough, so that the factored bending moment will be comparable to that developing in cases of commercial

buildings. Post-tensioning is preferred as it is in vogue, in construction of large span slabs.

II. MethodologyTo begin with, an R.C.C. FLAT SLAB was manually designed by using the limit state method based on IS: 456-

2000. Based on the steps & formulas involved, a design program was prepared in MS EXCEL. The veracity of the program

was checked by first designing the manually designed SLAB by using the program & comparing the results. Since in field, a

mix richer than M 30 is seldom used for R.C.C., the grade of concrete was maintained at M 30 for R.C.C.

An identical procedure was followed for PRESTRESSED CONCRETE FLAT SLAB. The manual design wasbased on the working stress method given in the book Prestressed Concrete by N Krishna Raju and checked by limit state

method suggested by the IS: 1343-1980. The program for designing the same was developed by using MS EXCEL & its

fidelity was checked by first solving the manual problem & comparing the results. Since the onus was on prestressing, the

slabs were designed for various concrete grades between M 30 to M 50, Table 11 in IS: 1343 was incorporated into the

program as a link so as to directly calculate the prestressing steel index. Design was carried out for parabolic strand profi le

only, which is the most popular one. Prestressed concrete flat slab of all concrete grades were designed for TYPE 2.

Programs were also prepared for estimating & costing. Rates are based on the latest CSR in Maharashtra. In case ofprestressed concrete, some of the rates were obtained from a well-known private Infrastructure company such as IRB and

LT.

III. Results And DiscusionTable 1 below gives the cost in rupees for various spans for both R.C.C. Flat Slabs in M: 30 grade concrete &

Prestressed Concrete Flat Slabs in M: 30 & higher grade concretes. Figure 1 below depicts the same statistics with the help

of bar charts.

Comparative Study of RCC and Prestressed Concrete Flat

Slabs
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Figure 2 below is a short form of Figure 1 where R.C.C. Flat slabs are compared with prestressed concrete flatslabs of different grades of concrete. Figure 3 below give percent saving in cost of construction with respect to higher values.

The cost of prestressed concrete flat slabs includes the cost of accessories like split cones, bearing plates, sheathing

tubes, grouting etc.

In our country, concrete grade higher than M 30 is generally not used in case of R.C.C. construction. But in

prestressed concrete construction concrete grades such as M 40 and M 50 are used.

Traditionally, column spacing and floor spans in these buildings such as commercial complex, shopping mall and

ware house etc has been in the range of 6 to 9 metres, to both contain costs and simplify construction. However, recentlythere is an increasing preference by building owners and tenants for large floor areas with column-free space and spans from

9 to 16 meters. This has focused the interest of designers and builders on methods of reducing costs and speeding

construction of long-span floors.

From the statistics, it is cleared that up to 9 m, Reinforced Cement Concrete flat slabs are economical as compared

to Prestressed Concrete Flat Slabs .Therefore in practice for spans up to 9 m, RCC flat slab dominates the Prestressed

Concrete flat slab.

Form spans 9m to 12 m, Prestressed Concrete flat slab becomes economical and as the span increases its

economical efficiency increases. This may not appeal much especially if we consider the hassles associated with prestressing

like skilled workmanship & need for superior quality control. But we must not forget that along with these minor

inconveniences prestressing delivers a structure that is better from limit state of serviceability & durability point of view.

Prestressed concrete flat slab were simultaneously designed in different grades for identical spans. The results showgradual increased in cost of flat slab with higher grades of concrete which differs in case of RCC. This is because of the large

difference in cost of higher grades as compared to lower grades of concrete irrespective of the saving of concrete due tosmaller depth of slab for higher concrete grades.

Table.1:Cost Comparison of R.C.C. And Prestressed Concrete Flat Slab

(+ve sign showing RCC Flat Slab is economical & -ve sign showing Prestressed Concrete Flat Slab is economical)

Spa

n (

m)

Conc

rete

Grad

e

Estimated

Cost of

Prestressed

Concrete Flat

Slab (Rupees)

Estimate

d Cost

Of RCC

Flat

Slab For

M30

Grade

Only(Ru

pees)

%

Differenc

e on the

basis of

Higher

Value

(%)

6M30M40

M50

10,41,832.5511,49,725.88

12,93,028.59

7,97,417.

3923.43

7

M30

M40

M50

15,47,927.56

14,89,880.00

16,76,070.00

12,75,25

8.6417.58

8

M30

M40

M50

20,05,632.48

21,57,895.70

21,76,305.96

19,34,49

2.043.49

9

M30

M40

M50

27,28,601.36

29,64,421.83

30,26,162.00

26,87,13

0.5 0

10M30M40M50

37,36,.27.8540,66,529.3742,92,180.92

39,76,10

0.49-6.04

11

M30

M40

M50

43,88,401.82

44,99,976.70

48,48,999.00

52,58,04

4.6-16.54

12

M30

M40

M50

56,04,387.18

57,64,089.07

60,83,029.00

76,17,20

2.13-26.42

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Figure 1: Variation of Cost with Span of Slab

Figure 2: Variation of Cost with Span of Slab

Figure 3: % difference on the basis of Higher value (RCC vs. PC for M30)

IV. ConclusionsBased on the study conducted, it could be concluded that RCC flat slabs are economical up to 9m span but beyond that

pre-stressed concrete flat slabs become a better choice. The cost advantage in percentage terms goes on increasing in favour

of prestressed concrete with increasing span. Besides, pre-stressed concrete flat slabs being thinner provide greater headroom

& result in lesser seismic forces. Better durability of prestressed concrete structures is already a well established fact.

V. Future ScopeCost comparison of RCC and prestressed concrete waffle slabs for spans above 10m.

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References[1.] DESIGN OF PRESTRESSED CONCRETE FLAT SLAB The South African Institution of Civil Engineering, South Africa, 1991.

[2.] Guide to Long-Span Concrete Floors, Cement and Concrete Association of Australia, August 2003.[3.] Analysis And Design Flat Slab Using Various Codes, M.Anitha, B.Q.Rahman, J. J .Vijay, International Institute of Informatio n Technology

Hyderabad, April 2007.

[4.] Analysis And Design of Flat Slab And Grid Slab And Their Cost Comparison Amit A. Sathawane & R.S. Deotale, Department of Ci vilEngineering, Yeshwantrao Chavhan College of Engineering Nagpur.

[5.]

Reynolds Reinforced Concrete Designers Hand Book.[6.] IS: 456-2000. Indian Standard Code of Practice for Reinforced Concrete.[7.] IS: 1343- 1980. Indian Standard Code of Practice for Prestressed Concrete (First Revision).

[8.] N. Krishna Raju, 2007. PrestressedConcrete, Fourth Edition, Tata McGraw- Hill Company Ltd., New Delhi.[9.] Dr. S.R. Karve & Dr.V.L. Shah, Limit State Theory & Design Of Reinforced Concrete.

[10.] B.N Dutta, 2009 Estimating and Costing In Civil Engineering, Twenty- Sixth Revised Edition UBS Publishers Distributors Pvt. Ltd. New Delhi.

[11.] Current Schedule of Rates (CSR), 2012-2013, for Public Works Region, Amravati.

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